1. Field of the Invention
This invention relates generally to the field of disk drives for mass information storage units for use in data processing systems and more particularly to a new and improved housing for disks used in such drives including integral means for reducing temperature differentials among disks.
2. Description of the Prior Art
Data processing systems typically include one or more mass data storage units in which data can be written on or retrieved from a magnetic medium. In modern data storage units, the magnetic medium typically may be deposited on and supported by an annular substrate such as aluminum. This disk is mounted in a drive in which it is rapidly rotated about its axis. The drive includes read/write heads which can be moved by an actuator in the drive across the disk surface to permit any one of a series of concentric annular data tracks to be accessed, the tracks being disposed on the substrate at differing radii. A drive may contain either a single disk or several disks stacked in spaced apart relation on a common spindle.
It has been an objective in recent years to increase the amount of data that can be stored in each disk, as well as the density at which the data is stored on the medium. This has necessitated an improvement not only in the magnetic medium itself, but also in the techniques used in manufacturing the drive, as rigid mechanical tolerances must be maintained to ensure that the read/write heads maintain the proper spacings over the disks. Furthermore, a housing is typically provided to prevent attracting dust from the surrounding air. If dust is permitted to accumulate on the disk surface, the accumulated dust would increase the height the read/write head must maintain above the disk, requiring the use of higher recording flux densities and reducing the available storage densities. The dust on the surface would also cause excessive wear on the head and slider.
To increase the reliability of the high-density mass storage disk, the so-called "Winchester"-type disk drives were developed in which the disks and the read/write heads and their actuating assemblies are all mounted in a housing assembly which is sealed to keep dust away from the disks. Filtered air may be directed over the annular disk surfaces to guard against the accumulation on the disks of dust which may seep into the housing. In prior art "Winchester"-type disk drives, as exemplified in U.S. Pat. No. 4,054,931 issued Oct. 18, 1977, the disk housing assembly comprises a heavy slab-like metal base plate and a separate cover, of lightweight material such as plastic, which completes and seals the housing. A gasket may be used between the base and the cover to enhance the sealing. The base plate is usually larger than the cover, but the cover extends over the portion of the base plate necessary to enclose the disks and the head actuator.
The disk housing assembly is mounted in the disk drive cabinet, which includes a drive motor for rotating the disks, typically through a belt which cooperates with a disk spindle pulley projecting through the bottom of the housing. The drive also typically includes power supplies for driving the motor and drive control logic circuitry to facilitate reading and writing the data from and onto the disks.
The filtered air, blown over the disks inside the housing also serves another purpose, in addition to dust removal. A substantial amount of heat is generated by the rotating disks, and the filtered air assists in removing the heat. A problem arises, however, when multiple disks are provided in the disk pack. The outer disks, and, in particular, the outermost surfaces of the outer disks, are able to dissipate more heat than are the inner disks and so generally are somewhat cooler than the inner disks. This temperature difference among the disks results in the inner disks expanding more than the outer disks, which results in the tracks on the inner disks being displaced at larger radii than the respective tracks on the outer disks. To compensate for this relative displacement, the tracks must be separated more than would be required if the temperature differential were reduced and the servo tracks must be broadened, reducing the amount of information storage available on each disk surface.
The prior art attempted to reduce the temperature differential by providing unused or "dummy" disks in the disk stack, such dummy disks being positioned above and below the active disks. This would essentially make all of the active storage disks in the stack inner disks and thereby reduce the temperature variation across such active disks. However, this technique does not eliminate the temperature differential problem, it merely shifts it as temperature differentials remain between the dummy disks and the active disks. Furthermore, the addition of dummy disks, which also are rotated in the stack substantially increases the load on the motor, especially during start up, when the motor is required to get the disks rotating rapidly in a very short period of time. For example, if four active disks are to be used, the addition of two dummy disks adds 50 percent to the mass and inertia of the stack, and increases the required motor power by at least that much.
The invention disclosed herein provides a new and improved housing including means for substantially reducing temperature differentials among the disks, without increasing the mass and inertia of the disk stake or adding to the load on the motor, thereby permitting respective tracks to be closer together and increasing the information storage density on the disks.